Axial piston pumps are currently known and widespread and are used for example in the field of high-pressure washers; they comprise an outer casing, which is constituted by a central pump body that is closed on one side by a corresponding head and is coupled, on the opposite side, to an electric motor that is provided with a cooling air duct.
Generally, together with the ordinary delivery and intake valves there is a high-pressure bypass valve (functionally connected to the delivery and the intake of the pump), which allows to recirculate the water inside the pump when the delivery is blocked, for example by releasing the button for blocking the nozzle of the lance-gun of the high-pressure washer to which the pump is applied.
Such high-pressure bypass valve is screwed into a complementarily threaded seat formed in the central pump body.
To prevent the motor from idling without pumping during water recirculation, a switching device is screwed onto the head of the high-pressure bypass valve and, by means of a transmission that is kinematically connected to the stem of the bypass valve, it operates a microswitch that is connected to the electric motor by means of electrical cables.
During the assembly of the pump, part of the time is dedicated to screwing the high-pressure bypass valve into the corresponding seat, part is dedicated to screwing the switching device onto the bypass valve, and part is dedicated to connecting the electrical cables to the switching device.
These operations occur also during disassembly, which is required for example during pump maintenance.
Generally, electronic components for controlling and managing the operation of the electric motor are associated therewith (and the electric cables that arrive from the microswitch are generally connected to said components). These components are fixed, generally in a rather inaccurate manner, on abutments formed on the outside of the air duct of the motor, and are scarcely protected against dirt, moisture, any accidental impacts during maintenance, et cetera.
The axial piston pumps thus described often have a device for injecting detergent into the water stream that flows from the delivery to the nozzle of the dispensing gun-lance.
These detergent injection devices are generally constituted by a Venturi tube, which is screwed into a complementarily threaded portion of the pump delivery tube, so as to produce a partial vacuum toward the nozzle of the dispensing gun-lance.
At the inlet of the Venturi tube (on the partial vacuum side), on the delivery tube there is a perpendicular connector onto which a check valve is screwed; a tube is screwed onto said valve and leads to a tank of detergent. The detergent injection device operates thanks to the partial vacuum produced by the Venturi tube, which allows to open the check valve and draw the detergent.
In this case also, as in the case of the bypass valve, it is not straightforward to provide correct assembly of the various components; moreover, it is complicated and expensive to provide the various threads on the delivery tube.
A similar problem occurs also for the delivery valves of the pump; each delivery valve is in fact generally screwed into a corresponding complementarily threaded cavity formed in the head of the pump.